feat: add clang

[dj8yfo]

this resolves near/cargo-near#255

tested on https://github.com/dj8yfo/compile_error/blob/3dd4741a53572a79497807b5d8806a3997f85c75/Cargo.toml#L15-L16

built from this image https://github.com/dj8yfo/cargo-near-image/blob/677b43f0778f43c939499429e3d566589ce98045/Dockerfile#L13

[Canvinus]

Do we also need clang for the cargo-near-commit Dockerfile?

[frol]

I was under assumption that Rustup ships clang as well since it heavily uses LLVM and it would make sense to use the matching LLVM for C dependencies, but it is not the case: rust-lang/rust#56371

@dj8yfo @Canvinus we may also consider adding clang++ (for C++ modules), though I cannot think of contract dependencies that would require C++ (in non-contract environment, there is only one C++ dependency that I know - RocksDB)

@race-of-sloths score 3

[race-of-sloths]

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Current status: executed

Reviewer	Score
@frol	3

Your contribution is much appreciated with a final score of 3!
You have received 35 (30 base + 15% lifetime bonus) Sloth points for this contribution

@frol received 25 Sloth Points for reviewing and scoring this pull request.

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